This invention relates generally to color reproduction techniques, and in particular to a method for determining and storing color printing information in the memory of a system for color reproduction.
One such color reproduction system is shown and described in Clark et al Ser. No. 292,293 filed Aug. 12, 1981, now abandoned entitled "Method of Color Conversion with Improved Interpolation" and assigned to the assignee of the instant application. This system utilizes a memory in which is stored a set of corrected color component values for reproducing a fraction of the total number of possible input colors. Corrected values for the remainder of the input colors are generated by an interpolative process based upon the contents of the memory. The developed corrected values represent, for example, engraving information in a rotogravure printing system and represent ink values for each of the printing primary colors yellow, magenta and cyan, or Y,M,C, as well as black, or K, to allow reproduction of an input color.
In order to reproduce accurately an input picture element, or pixel, it is necessary to load the memory with values which account for the characteristics of the particular inks and paper to be used in the final printing process. One prior process for generating a set of corrected values and for using these values to perform color reproduction is shown in Korman U.S. Pat. No. 3,612,753. A large number of patches, e.g. 512, of arbitrary colors are printed using the particular inks and paper to be used in the final printing process. The color component engraving values required to print each patch are noted. The patches are scanned by a densitometer to develop scanned values. The engraving values and scanned values are combined in a memory such that the engraving values are addressed by the scanned values. The input matter to be reproduced is scanned and the resulting values are used to address the memory. The values from the memory are used in conjunction with interpolated values to engrave printing plates to allow reproduction of the input matter.
Another type of process for developing corrected values and for using the values to engrave printing plates is described in Hardy et al U.S. Pat. No. 2,434,561. A color chart of nine colors is printed using the inks and paper to be used in the final printing process. The colors are formed from the printing primary color components, i.e. cyan, yellow and magenta, and from combinations of these colors. The engraving values required to produce these colors are noted. The color chart is then scanned by a densitometer to obtain scanned values for each of the nine color patches. The engraving and scanned values are inserted into a set of transformation equations, i.e. Neugebaurer's equations, and the equations are solved for the constants.
Input matter to be duplicated is then scanned to obtain scanned values for each pixel of the input matter. Using the scanned values of the pixels and the constants obtained by solution of the transformation equations, the transformation equations are solved a second time to calculate the engraving signals which are required to reproduce the input pixel colors. A set of color plates is then engraved using the engraving signals.
Such processes for generating corrected color values are cumbersome and/or exceedingly complex. The first requires the printing and scanning of a large number of color patches while the second requires a set of complex transformation equations to be solved twice to generate the corrected color values.